Semiconductor, thermocouple, or resistor sensors in chip form, for instance, are used for precise measurement of temperature in process industry.
Sensor technology used in the prior art is often based on thick-film technology, wherein an active element is made by metallizing the element on the surface of a ceramic plate chemically, by evaporation or sputtering.
In the prior-art solutions, between the surface being measured and the measuring element, there is, thus, ceramic material that is usually dimensioned in the range of 2.5×2.0 mm with a thickness of approximately 0.7 mm. Measuring conductors with a typical diameter of approximately 0.2 mm are connected to the measuring element.
A problem with the prior-art solutions is conducting heat at an as small temperature difference as possible to the measuring element through an aluminum oxide layer. Another problem with the prior-art solutions is heat conduction away from the measuring element through connection conductors, the prevention of which is problematic. The connection conductors need to be relatively thick in comparison with the surface area of the chip. The diameter of the connection conductors cannot be reduced very much due to connectivity in practice. If the diameter of the connection conductors is reduced too much, conductor resistance at the measuring element begins to increase in a disturbing manner.
Solutions in which sensors are manufactured in the form of chip resistors are also known in the prior art. In solutions of this type, solder terminals are metallized at the ends of a ceramic chip to transfer the measuring signal onward.
In both above-mentioned prior-art constructions, heat loss at the measuring element causes a significant measuring error, when the temperature difference increases between the temperatures of the process being measured and the environment.